This proposal is based on the premise that complex cognitive disorders in brain-damaged subjects can be analyzed in an objective, quantitative manner. Such precision is necessary to get beyond qualitative descriptions and to probe for underlying mechanisms. In the syndrome of unilateral spatial neglect, patients fail to orient towards, respond to, or act on stimuli in space contralateral to their lesion. Neglect may reflect a disorder in the ability to direct attention into contralateral space. During his fellowship, the Candidate discovered that abnormal behavior of patients with neglect may be precisely captured by the simple mathematical formula, psi = K(phi)beta. This power function relates the quantity of stimuli of which these patients are aware (psi) to the quantity of stimuli presented to them (phi). The constant (K) and the exponent (beta) are empirically derived. The observation is of particular significance because the psychological experience of sensations in normal subjects is also related to objective measures of sensory magnitude by power functions. Power function analyses uncover specific quantitative ways in which neglect behavior is similar to and deviates from normal. The present investigation will extend preliminary observations by testing left and right brain damaged patients and normal subjects on line bisection, cancellation and reading tasks. Power function analyses will be applied to these tasks to examine 1) the relationship between the function and the anatomy of attentional networks, 2) develop a methodology to investigate patterns of recovery after acute brain damage, 3) assess disturbances of attentional capacity after damage to attentional networks, and 4) clarify the consequences of such damage to mental representations. It is anticipated that the Specific Aims proposed will establish power function analyses as a novel and precise method to investigate mechanisms underlying the syndrome of unilateral spatial neglect.